Electromagnetic deflection coil



Oct. '31, 1961 c. R. CORPEW 3,007,087

ELECTROMAGNETIC DEFLECTION con Filed June 4, 1958 3 Sheets-Sheet 1 CONTROL INVENTOR. C HAQLES l2. CORPEW. BY W Oct. 31, 1961 c. R. CORPEW 3,007,087

ELECTROMAGNETIC DEFLECTION COIL Filed June 4, 1958 5 Sheets-Sheet 2 INVENTOR. CHARLES l2. COIZPEW.

Oct. 31, 1961 c. R. CORPEW 3,007,087

ELECTROMAGNETIC DEFLECTION con.

Filed June 4, 1958 3 Sheets-Sheet 3 1 H I I I |g 5a l |g =|b INVENTOR. CHARLES Q. COQPEW. BY 5mm- Zgwf United States Patent F 3,007,087 ELECTROMAGNETIC DEFLECTIQN COIL Charles R. Corpew, San Diego, Calif., asslgnor to General Dynamics Corporation, Rochester, N.Y., a corporation of Delaware Filed June 4, 1958, Ser. No. 739,713 6 Claims. (Cl. 317-200) The present invention relates to an improved electromagnetic deflection coil and more particularly, to an electromagnetic deflection coil having an improved core construction and an improved wiring arrangement within the core. The improved coil is capable of furnishing a uniform flux field for deflecting an electron beam in a cathode ray tube while also providing a short flux time lag. I

Electromagnetic deflection coils are generally used to establish electromagnetic fields of influence to control electron beams projected in a cathode ray tube, where the coils are mounted around the neck of the cathode ray tube. In some specific uses of cathode ray tubes, it is necessary to have a uniform field pattern capable of providing distortionless beam deflection for large electron beam cross sections, and also having a rapid flux decay time. For example, in a random address type of display, such as in a shaped beam cathode ray tube of the type disclosed in Patent No. 2,761,988 issued to Joseph T. McNaney, and assigned to the common assignee hereof, it is desirable to accurately and rapidly deflect the shaped beam, which has a cross sectional dimension larger than ordinary, to a particular point on the screen of the tube giving a distortionless display. A large flux time lag that is present in known coils and which is caused by the time required for flux decay of the main field and extraneous fields, has been a limiting factor in permitting rapid positioning of the beam accurately on the screen of the tube. Also, non-uniformity of the deflection field in the known coils has, when using the larger' cross section beam, caused the character displays on the tube screen to be distorted. In the known coils, of either the air core type or of the iron core type, flux lines are generally set up outside the coil due to the generation of the field within the coil or due to the generation of a field by eddy currents created within thecore. This resultant outside field contacts other metal parts in proximity to the cathode ray tube, causing eddy current to be generated in these other outside metal parts. 'These eddy currents in outside metal parts and the eddy currents created within the core create flux fields which continue to circulate or oscillate after the current has been changed in the windings of the coil. Since these eddy currents and their corresponding extraneous fields have a longer flux time lag than that of the main field within the coil, they cause the electron beam to be adverselydeflected after the influence of the main field has been removed. This has an obviously detrimental etfect,'as it creates what appears to be distortion in the image displayed on the screen of the cathode ray tube and also causes the image to be incorrectly positioned. To reduce this distortion effect, it has been necessary to. lengthen the time interval between successive displays in the high speed linear deflection of the electron beam.

-Iron cores have often been used in electromagnetic deflection coils, since they are capable, in many instances, of increasing the total magnetic flux in the main field and aid in guiding the flux to the region where it is needed. Howeveniron cores tend to increase the inductance of the coil with its attendant disadvantages of a longer RLC circuit time constant and also iron cores increase the magnitude of eddy currents. While laminating iron cores have reduced somewhat the magnitude of the eddy currents, the high inductance is still present.

3,007,087 Patented Oct. 31, 1961 Further, the primary reason and benefit for laminating the iron core is to reduce the power loss resulting from the large eddy currents. This power loss is a problem that is present in conventional uses of deflection coils. However, eddy currents cannot be reduced by increasing the resistance to current flow in the core through laminations, to the degree required in special applications of deflection coils, such as in shaped beam cathode ray tubes, where the extraneous fields caused by the eddy currents is the primary problem and not the power loss.

The present invention concerns an electromagnetic deflection coil of the cylindrical type having an annular outside core forming a close fitting outer enclosure around series aiding field windings. The core is constructed of ferrite material which may take the form of any ferromagnetic material of the type set forth on pages 490 and 491, Solid State Physics by Adrianus J. Dekker, printed by Prentice-Hall, Inc. The aforesaid pages set forth the general properties of ferromagnetic materials and their composition. Ferrite material is capable of providing an enclosed flux path for the return of flux lines thereby permitting the series aiding field to be concentrated in an air path across the neck of the tube while not increasing the inductance appreciably and substantially eliminating the eddy currents. Thus, the present invention overcomes the aforesaid difliculties encountered with prior art electromagnetic coils.

The ferrite outer core is provided with a cylindrical recessed portion within its longitudinal extremities onto which or within the confines of which there is disposed a predetermined pattern of conductive windings. These windings, may, if desired, be etched Onto the inner surface of the core body itself, or, they may be wire conductor mediums disposed on an insulated surface positioned adjacent the core body. The windings are of a predetermined size and have a predetermined geometric disposition which is contained completely within the confines of the cylindrical core. As the windings through which the current flows create their fields, the pattern so created is established within the core and its immediate inner dimensions. The particular geometric disposition of the windings aids in establishing a desired uniform field pattern.

z'In addition to the objects and advantages stated, it is an object of the invention to provide a new and improved electromagnetic coil capable of generating a flux pattern substantially devoid of external extraneous fields.

' It is another object of the invention to provide a de flection coil wherein the coils core houses within its inner dimensions, a geometric pattern of electrical conductors for establishing a uniform electrical magnetic field.

It is another object of the invention to provide an enclosed flux path which cuts down the strength of the resultant field outside the coil and does not experience large eddy currents therein which would increase the flux lag time of the coil.

-It is another object of the invention to provide a coil utilizing series aiding windings which may be spaced within the coil to provide selective distorted fields.

It is another object of the invention to provide a coil capable of providing a controlled flux decay time for the deflecting fields within the core.

It is another object of the invention to provide an electromagnetic coil capable of providing a rapid flux decay time with a uniform field while having a small inter-diameter.

Objects and advantages other than those set forth above will become apparent when read in connection with the accompanying specification and drawings, in which:

FIGURE 1 is a perspective view of a shaped beam cathode ray tube with a specific embodiment of the invention mounted thereon;

FIGURE 2 is a perspective view of a specific embodiment'of the electromagnetic deflection'coil;

FIGURE 3 is a perspective view of two spiral winding units placed in series aiding position;

FIGURE 4 is a sectional portion of a spiral winding unit illustrating the manner of its construction;

FIGURE 5 is a Schematic of a to plan'view' of a spiral winding unit placed in' a flat position;

FIGURE 6 is a schematic of a cross-sectional view of the electrode magnetic deflection coil;

7 FIGURE 7 is a schematic of the arrangement ofwin'dings in a coil under cosine distribution; I

FIGURE 8 is a graph for illustratingthe relationship of magneto-motive force with the length of the flux'path' through an electromagnetic deflection coil when the windings are distributed in a perfect cosine distribution;

FIGURE 9a illustrates the direction of current in 'the angled portion" of the spiral windings as shown in FIG- URE 5, with its components arranged in their effective positionfor creating effective magnetic flux in the coil;

FIGURE 91) illustrates the direction of the flux-fields created by the currents shown in FIGURE 90;

FIGURE 10 shows in schematic the overlapping of successive layers'of spiral winding units to obtain the 90 cross over relationship between windings.

Referring to FIGURE 1, a cathode ray tube of the shaped beam variety is provided with a cylindrical neck portion and a screen surface 16. The electron beam 23 to be deflected is generated by an electron gun'17 and is shaped into a particular character by shaping matrix 18. The shaped beam is deflected back to the longitudinal axis of the tube by convergence coil 19 and oriented on the longitudinal axis by the electrostatic deflection plates 21 and then finally deflected to a particular portion on the screen of the tube by the electromagnetic deflection coil 22. In deflection of the shaped electron beam by deflection coil 19, more critical considerations, than would normally be taken in an ordinary cathode ray tube, must betaken with respect to the field uniformity and the flux lag time. The uniformity of the field must be suffici'ent to preclude distortions arising from pincushion fields and barrel shaped fields.

. A flickerless display of several characters on'the tube screen 16 at any one instant requires a high speed linear deflection of the electron beam. In accomplishing the aforesaid high speed deflection, it is desirable that there be no extraneous electromagnetic flux remaining in theneck ofthe tube after the positioning of the character image on the screen; because, such remaining flux will efiect the positioning of the subsequently displayed character. Such extraneous fields will add to or subtract from the subsequent main deflecting field to cause the subsequently displayed character to be incorrectly positioned. Accordingly, it is obviously desirable that the flux time lag of the deflection coil have as short a time response as is possible and also, of course, provide as uniform a' field as possible.

The electromagnetic coil 22 shown in FIGURE 2, has an outer core27 and inner'windings 28'. The core may be constructed of ferromagnetic material capableof providing a return path for the flux generated by the field in the manner shown in FIGURE 6, thus, providing a closed electromagnetic circuit. The core construction provides a high resistance path for any eddy currents that may be generated within the core itself due to the main field. Thus, the core has the ability to provide a good flux path for the fields created by the main field while substantially eliminating the generation and perpetuation of eddy currents. It therefore has the advantage over the laminated core in that it reduces eddy currents to a much greater degree and also has a low inductance factor. While the core restricts the possibility of generating a field external to the core itself, it also forms an effective shielding for the flux within its confines, precluding the effect of any external field created by currents in external metallic members in proximity to the cathode ray tube. This is of an extreme advantage in reducing and controlling the flux lag time inasmuch as the delay time for extraneous fields created by the aforesaid eddy currents have a flux lag time which exceeds that of the fields created by the coil itself.

Thewindings-28 are ofthe series aidingtype and have a semicylindrical shape for insertion within the inner surface of the cylindrical core (see FIGURE 3). They may consist of conductors etched into the inner side of the core body itself, or they may consist of wires disposed upon a suitable insulating medium such as by printed'circuit techniques and then inserted either singly or in layers on the inner surface'of the cylindrical core. As shown in FIGURES 3, 4 and 5, the conductors or wires 35 which may be'of copper or the like, may be deposited ona sheet of material 34 such as Teflon or the like in a predetermined geometrical configuration. The windings 28 have a longitudinal length that is smaller than the length of the core 27. Accordingly, the fields generated by the windings are restricted to the internal volume of the core to a high degree.

FIGURE 3 illustrates a portion of windings 28 which consists of individual spiral wire units, 30 and 31, oriented: in the position they have when inserted in the cylindrical Winding units 30 and 31 are mounted in series core. aiding relationship with the current passing in at I and out at I as shown. The connection 29 between spiral units 30 and 31 gives a series current relationship through both of the spiral units shown in FIGURE 5. However, each winding unit may be energized separately by breaking the connection 29 and connecting each of the separated wires directly to the current source. A complete winding unit 28 for providing both horizontal and vertical deflection would consist of at least four winding units as illustrated in FIGURE 2 and FIGURE 6. Thse units 30, 31 and 32, 33 provide a field capable of deflecting the electron beam in either a horizontal or a vertical direction.

Each unit is mounted in a off-set relationship, thus, providing-a horizontal and vertical deflection field. The number of turns in each spiral winding unit may be determined both by the intensity of the field desired and that required to give the desired configuration to provide a uniform field. The size of the spiral wires may also determine the strength of the field generated, as it would control to a certain degree the amount of current that would flow through the windings. Also, the number of separate layers may also be used to vary the strength of the field and the size of the conductors desired. The width of each continuous conductor 36 is' the same for each spiral unit, and the distance between each turn of wire in the spiral is constant. Generally, the spiral conductors or Wires-are increased in width with each particular layer.

The outer core 27 as shown in FIGURE 6, tightly en'- closes the windings 28. This aids materially in restricting the field to an area enclosed by the cylindrical shell. The field pattern shown illustrates the direction of the flux field H when windings 30 and 31 are energized. In this semi-cylindrical spaced relation, the fields of the twowindings are aiding in setting up the flux H in the same direction through the center of the coil, thereby creating a south pole onthe side of winding unit 31 and a north pole on the side of winding unit 30. The flux after pass ing through the center of the coil, is returned through the outer core 27 in the manner shown. Thus, the entire strength of the field is contained and passed through the air gap, inasmuch as the flux H passing through the air core is returned through the outer core which path entirely encloses the inner winding. Also, any extraneous fields occurring external to the coil, will be unable to appreciably effect the beam in its passage through the coil because the ferrite core is impervious to these extraneous fields and thus, shields the beam from such fields within the volume of the core. Further, since the ferrite material has a high resistivity, these extraneous fields cannot effectively cause eddy currents in the core.

The particular geometric pattern in which'the wires are placed in the spiral on the insulated sheet, or, on the inner surface of the core is shown in FIGURE 5. It has been found by experimentation that this octagonal geometric pattern gives the desired uniform field across the neck of the tube capable of providing deflection of the electron beam to the far corners of screen 16 with substantially no distortion. Inasmuch as the uniform field H has been obtained by experimentation through numerous experiments with the device, it is not known the exact theoretical basis for why these results were obtained. Accordingly, the following theoretical explanation, generally known as the cosine theory, is only advanced as a possible theory for explaining the results obtained and is not deemed to be a limitation upon the present invention, inasmuch as the theoretical approach has never been completely tied in with the results obtained. Generally, in the use of series aiding fields, it has been found that to obtain a uniform field across the area between the windings, it has been necessary to space the windings substantially as shown in FIGURE 7. This spacing has been accomplished by spacing the windings a greater distance apart as the circumferential distance from axis 29 is increased. The conducting wires are normally placed within slotted recesses in the core. In FIGURE 7, L is the length of the magnetic field, D is the diameter of the inner circumference of the windings or core and the angle a is the angle of the arc as shown. With the foregoing parameters identified, the following relationships are normally deemed applicable under the cosine theory. The total number of windings positioned around the circumference from a= to a=90 should be proportional to the sine of a. The density of the windings should be proportional to the cosine of a and the magnetomotive force should be proportional to the length of the flux path L. Accordingly,- the best winding arrangement under this theory would be where the mag-netomotive force along line L is proportional to all lengths of the flux path L and varies substantially with the curve shown in FIGURE 8.

While this theoretical approach has not been found applicable in all situations, it has been found to be generally a good basis for determining possible results from winding arrangements. With respect to FIGURE 5, the angle 'a=0 to a=90 as set forth in FIGURE 7 is shown in relation to the particular spiral unit shown in FIGURE v5. The current in each of the individual wires of the spiral is the same, inasmuch as all of the wires are connected in series. The parallel wires 37 of the spiral generates a magnetomotive force H which is capable of deflecting the electron beam, whereas, the flux H generated by the parallel lines 38 is in a direction along the longitudinal axis of the tube and has a focusing or defocusing effect, but does not function to appreciably deflect the beam. The angular wires 36, which connect parallel wires 37 to the parallel wires 38, carry a current I (see FIGURES and 9a), which causes a flux field H shown in FIGURE 9b. This current I and'its respective flux field H can be broken down into two components I I and H H to illustrate its effect in the deflection of the beam. The field H created by current I causes deflection of the beam in the same manner as the field created by the current in wires 37, and the field H does not deflect the beam the same as the field created by wires 38. Accordingly, the strength of the deflecting flux in the area B is varied in substantial proportion to the length of the flux path L. The angle of intersection of the wires at the 8 points of intersection is 45 for the specific embodiment. In the construction of electromagnetic deflection coils, the length of the insulation sheet 31 and the windings 35 are limited by the circumference of the neck of the tube, because in using series aiding fields as well as other fields, it is desirable to placethe windings of the coil as near the neck of the tube as possible. Since the inter-circumference of the coil is determined by the outer circumference of the neck of the tube, the circumferential while still permitting a strong uniform field. Further,

the coils may be positioned in their off-set relationship in the manner shown in FIGURE 10, wherein the angled wires 36 of overlapping spiral windings 30, 31 and 32 have an intersecting angle of 90. This elfectively reduces cross currents since the currents generated in each winding by flux fields in the overlapping winding will be in opposition. Another advantage of the present invention is that varying the distance 42 in FIGURE 3 between spiral units 30 and 31 will vary the uniformity of the flux field, thereby making it possible to obtain a desired distortion. By making the space 42 between the ends of spiral 30 and 31 larger, a barrel shaped field will be obtained, whereas by narrowing the distance between 30 and 31, a pincushion field is obtained.

The particular embodiment of the invention illustrated and described herein is illustrative only and the invention includes such other modifications and equivalents as may readily appear to those skilled in the art, within the scope of the appended claims.

I claim:

1. In an electromagnetic deflection coil having series aiding windings, winding units being disposed in complementary disposition and in spaced relation to each other for creating a flux field within said coil, each of said units having a conductor octagonally arranged in spiral concentric turns.

2. In an electromagnetic deflection coil having series aiding windings, winding units being disposed in complementary disposition and in spaced relation to each other for creating a flux field within said coil, each of said units having a conductor octagonally arranged in spiral concentric turns, said conductor having a uniform width with equal spacing between said turns.

3. In an electromagnetic deflection coil having series aiding windings, winding units being disposed in complementary disposition and in spaced relation to each other for creating a uniform flux field within said coil, each of said units having a conductor octagonally arranged in spiral concentric turns, said windings being capable of providing a predetermined field distortion in response to varying said spaced relation.

4. In an electromagnetic deflection coil having windings, said windings comprising layers of winding units being disposed in complementary semi-circular disposition and in spaced relation to each other for creating a flux field within said coil, each of said units having a conductor octagonally arranged in spiral concentric turns, each of said conductors in each of said units having a uniform width throughout its length and having equal spacing between said turns, said width of said conductors increasing in size with each succeeding one of said layers. 5. An electromagnetic deflection coil having layers of series aiding windings for creating a flux field within said coil, each of said layers comprising two winding units being disposed in complementary semi-circular disposition and in spaced relation to each other, each of said units having a conductor octagonally arranged in spiral concentric turns, each succeeding one of said layers being displaced substantially 90 with its successive layer, said succeeding layer overlapping said successive layer in a manner providing for parallel conductors in said octagonal spirals of each unit to cross over at a normal angle thereby reducing cross currents in said units.

coil; each" of said layers comprising tvvdvvinding units'being di'spos'e'diii complementary sefni-circular dispositionand inspaced relation toeach' other, each of said units having a conductoroctagonally arranged in spiral'com centric turns, said windingsb'eing capable of providing a predetermined field distortion in response to varying said spaced relation, each succeeding one of said la'y'ers bein'g' displaced substantially "90 v'vith'its successivelayer, said" succeedinglaver overlapping said successive layer ina ni'arfner providing for parallel 'wires in said octagonal spiralsof eachunit to cross over at anormal angle thereby reducin'g-cr'o'ss currents in said units;

References Gited-in the file of this patent- UNITED STATES PATENTS 2,605,433 Friend- July' 29, 1952 2,689,923 Janssen Sept. 21, 1954 2,730,642 Grosjean Jan. 10, 1956 2,830,212 Himlt- Apr. 8, 1958 2,831,135 Hanlet Apr. 15, 1958 2,831,136 Hanlet Apr. 15, 1958 2,855,530 Hamann Oct. 7, 1958 

